A field emission display device (hereinafter referred to as “FED”) is a representative display device for displaying an image by applying a strong field on an emitter which is an electron emission source to provide the electrons with a tunneling effect, moving the emitted electrons through vacuum, and colliding the electrons with a phosphor screen formed with an anode electrode to emit the light and express the image.
Carbon nano tubes (CNT) have recently emerged as a potentially useful electron emission source. In particular, carbon nano tubes are anticipated to be an ideal electron emission source since they feature a low work function, the resultant electron emission source can be driven by applying low voltages, and the method of fabricating the same is not complicated. They will thereby offer advantages to realize a large size panel display.
Generally, a field emission display device having carbon nano tubes as the electron emission source constitutes a triode structure in order to control electron emission. The electron emission layer of carbon nano tubes is formed by either a thin film coating process using vacuum evaporation, or a thick film coating process using a printing composition. The latter process includes the steps of preparing a composition consisting essentially the carbon nano tubes and printing the composition on a cathode electrode to provide the electron emission layer. The thick film coating process therefore is advantageous in that it involves a simple manufacturing process that is suitable for mass production relative to that of the thin film coating process.
The carbon nano tube electron emission source is formed by preparing a composition comprising carbon nano tubes, a binder, and a solvent; screen-printing the obtained composition on the electrode; and baking it at a high temperature of 400° C. or more under an air atmosphere.
The binder may include any thermal decomposing resin such as acrylate, acryl, or ethyl cellulose (EC). If only acrylate resin is employed as the thermal decomposing resin, the carbon nano tube composition is advantageously well patterned, but the current density disadvantageously is decreased to a value such as 20 μA/cm2 at 7.5 V/μm upon application to a triode carbon electron emission source.
On the other hand, if acryl or ethyl cellulose is employed, the current density is advantageously increased to 100 μA/cm2 or more, but it disadvantageously shrinks by the thermal decomposition after the baking process, and the attachment strength is weakened between the pattern and the substrate. Further, the composition is inevitably contacted with a photoresist after exposing with an ultraviolet ray during the patterning process. Disadvantageously, the reaction between the composition and the photoresist causes a short circuit between a gate electrode and a cathode electrode. When the composition is employed for the triode carbon electron emission source, it causes a problem in that the working voltage may be increased since the obtained film is too thick and the distance to the gate is too far.
As a result, any one resin selected from the group consisting of acrylate resin, acryl resin, and ethyl cellulose is employed for fabricating the triode carbon nano tube, and it is difficult to satisfy both the patterning characteristic and the current density at the same time.
In addition, a structure has been proposed with a resistive layer between a cathode electrode and an emitter in order to improve the uniformity of electron emission (U.S. Pat. No. 5,194,780). However, this method requires additional coating and patterning processes for providing the resistive layer, rendering the manufacturing process more complicated and decreasing the yield.